1. Field of the Invention
The present invention relates to an impedance standard substrate for a vector network analyzer, and more specifically, the present invention relates to an impedance standard substrate for a vector network analyzer, which is provided with contacts disposed on opposite sides thereof.
2. Description of the Related Art
Vector network analyzer is well known, for example, such as those disclosed in U.S. Pat. No. 6,348,804 entitled “Vector Network Analyzer,” U.S. Pat. No. 5,047,752 entitled “Verification And Correction Method For An Error Model For A Measurement Network,” and U.S. Pat. No. 4,858,160 entitled “System For Setting Reference Reactance For Vector Corrected Measurements.”
Those vector network analyzer mainly utilizes one or two RF (Radio Frequency) sources for generating high-frequency signals, and two measuring ports for transmitting the signals to a DUT (Device Under Test). In a test set, directional couplers or directional bridges are used to separate the signals sent to the DUT, i.e. incident signals, and the signals reflected from the DUT, i.e. reflective signals. Both of the incident signals and the reflective signals are converted to low-frequency signals by a downconverter consisting of a local source and a mixer, and then the processes such as filtering and amplifying the signals, converting to digital signals and displaying the measuring data are carried out.
High-frequency measurements require highly accurate measurements of complex (magnitude and phase) reflection and transmission coefficients. The measurement system is calibrated by complex error factors.
These error factors are conventionally determined by measuring the known impedance standards. Although different impedance standards may be used, the ones most commonly employed are the open-circuit, short-circuit, load-circuit, and thru-circuit. The measuring port of the vector network analyzer is provided with a probe for respectively touching the contacts of the open-circuit, short-circuit, load-circuit, and thru-circuit, thereby determining the error factors and calibrating the vector network analyzer.
Those impedance standards are typically disposed on a single surface of a substrate which is referred to as an impedance standard substrate. However, in practical measurement of a DUT such as a BGA (ball grid array) substrate of a BGA package, since the BGA substrate has contacts disposed on two sides thereof, one of the probes in the vector network analyzer has to be turned by 180 degrees for measuring the BGA substrate after the measurement on the single surface of the impedance standard substrate has been done. Particularly, for the thru-circuit, the two probes of the vector network analyzer have to be in contact with either end of the thru-circuit at the same time and the impedance standard substrate in prior art is not provided with contacts disposed on both sides thereof, so such a turning action of the probes cannot be avoided. Such a turning action not only requires a complex mechanism, but also influences the preciseness of the measurement.
Accordingly, there exists a need for a two-side impedance standard substrate with impedance standard contacts disposed on both sides of the substrate for facilitating the calibration of the vector network analyzer.